Magnetic resonance imaging systems rely on the tendency of atomic nuclei possessing magnetic moments to align their spins with an external magnetic field Only nuclei with odd numbers of nucleons have a magnetic moment, so only these nuclei can be detected and imaged. Hydrogen has one nucleon, a proton, in its nucleus and is the primary nucleus imaged at this time in medical practice.
The most common isotope of oxygen, oxygen-16, has an even number of nucleons and hence, cannot be imaged in a magnetic imaging system. Oxygen-15 is unstable (radioactive) and is used in other imaging techniques which subject the host to a radiation dose. Oxygen-17 is stable and meets the odd nucleon number critera necessary for magnetic resonance imaging, but it is extremely rare and hence has not been utilized since relatively large quantities would be needed.
Prior to the present invention, the oxygen-17 isotope had only been utilized for diagnostic purposes by administering the isotope into a warm blooded animal in the form of water. By following the distribution of water in the body using magnetic resonance imaging it was possible to trace the location of the oxygen-17 isotope.
Some of the earlier investigations on NMR study of the protein transfer in water as reported by S. Meiboom, J. Chem. Phys., 39, 375, 1961, showed that at neutral pH, protein transverse relaxation time (T.sub.2) is significantly shorter than longitudinal relaxation time (T.sub.1). The author suggested that this difference is due to the naturally occurring H.sub.2.sup.17 O isotope (0.037 at. ) in the H.sub.2.sup.16 O and at a neutral pH this effect is greater due to scalar coupling interactions between the guadrupole .sup.17 O and protons. Meiboom further demonstrated that at any pH above or below the neutral pH the resident lifetime of the protons on 170 (spin=5/2) is too short to produce any enhancement of relaxation. In contrast to T.sub.2, T.sub.1 was not affected by enrichment or pH.
In work by Hopkins et al Mag. Reson. Med. 4, 399, 1987, there is reported the enrichment effects of H.sub.2.sup.17 O on protein solutions and living tissues which is in agreement with Meiboom's protein exchange rate studies.
In the Research Resources Reporter, Aug., 1988, it is disclosed on page 12 that fluorine was used in conjunction with magnetic resonance imaging (MRI) to obtain information about blood flow. It was indicated therein that accurate information could be obtained by the study of several nuclei simultaneously and blood flow could be measured on a real-time basis. Dr. J.S. Leigh, one of the coauthors, disclosed that by combining MRI and magnetic resonance spectroscopy (MRS), one could obtain an image of the inside of a person and obtain a very complete biochemical analysis of what is there.
However, as previously indicated, administration of the oxygen-17 isotope had only been effected by the use of water containing the isotope. Accordingly, one or more of the following objects will be achieved by the practice of this invention. It is an object of this invention to provide a method for introducing oxygen-17 into tissues for imaging in a magnetic imaging system. Another object of this invention is to provide a method for detecting localized metabolic activity under physiological conditions by monitoring the in vivo production of H.sub.2.sup.17 O metabolite in tissue utilizing oxygen-17, promoted proton T.sub.2 relaxation enhancement. A further object of the present invention is to provide a novel complex of the oxygen-17 isotope and a biologically acceptable liquid emulsion carrier which can be administered to a warm blooded animal to detect localized metabolic activity. A still further object is to provide a novel complex of the oxygen-17 isomer and a perfluorinated compound. Another object of this invention is to provide a complex of the oxygen-17 isomer and perfluorotributylamine. Another object of this invention is to provide a method for preparing the novel complex of this invention. A still further object of the invention is to provide a method for introducing the complex of the oxygen-17 isomer into a warm blooded animal for the detection of localized metabolic activity. Another object is to obtain information about tissue perfusion by imaging fluorine-19 and oxygen utilization by imaging H.sub.2.sup.17 O as a metabolite. These and other objects will readily become apparent to those skilled in the art in the light of the teachings herein set forth.